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Re: ISO C99 support in <math.h> for C++98

On 2016-03-22 09:52, Andre Vieira (lists) wrote:
On arm and aarch64 the libstdc++ test
26_numerics/headers/cmath/ has been
failing with (among others) the following errors:
Since the only code my gcc-5 and trunk builds share is newlib I suspect
it might be caused by it. I had a look at cmath and found that the
macros mentioned above are undef'd if the condition
_GLIBCXX_USE_C99_MATH holds true. This is defined as
_GLIBCXX98_USE_C99_MATH if -std=gnu++98 is passed and in my latest
builds _GLIBCXX98_USE_C99_MATH is no longer being defined in
c++config.h. This define is set by gcc's configure step 'Checking for
ISO C99 support in <math.h> for C++98' which used to succeed but now fails.

I did get a bit lost after locating the code to check this in
gcc/libstdc++/acinclude.m4 as it seems it tries to compile a file with
all the functions (macros in C99), that are undef'd in cmath if
_GLIBCXX_USE_C99_MATH, which isn't happening... So apparently during
configuration it seems include math.h does not define this set of
functions, so _GLIBCXX98_USE_C99_MATH is never defined and thus the
macros for these functions are never undef'ed in cmath, where all of a
sudden they seem to be defined.

Does anyone have an idea whats going on here? I wanted to try with
earlier commits of newlib to maybe identify what change was responsible
for this new behavior, but I am failing to build due to the
configuration scripts needing regeneration and I wasn't able to
regenerate them. I tried a sequence of commands that used to work in the
past but they no longer do :(

We also had issues enabling C99-in-C++ on Cygwin (which is based on newlib), which required a few patches:

It is on my to-do list to get this working on newlib targets once we have a snapshot with the new feature test macros.


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